Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species

It was laid down as a principle generally followed in cases of double extra appendages, that the three terminations, when extend,.,!, stand in the same plane, and the chief feature which distinguishes the two following cases is that the three terminations are not in one plane. Moreover, though the two supernumerary tarsi are a complementary pair, and together with the normal tarsus are arranged as a series of images, yet in order to produce the arrangement of the present cases the planes of reflexion would not be parallel to each other (as in Fig. 154) but inclined in the manner to be described.

'776. Calathus graecus £ (Carabiche): left anterior tibia bearing a pair of supernumerary tarsi compounded together. Tlie diagram, Fig. 169, I, shews, in projection, the relations of the parts round the tibial apex. As has been explained, the posterior spurs P1, P" and P1 are really much central to the apex, but they are here represented as if they were projected upon the apex. The head of the tibia is produced posteriorly into a long and narrow process which is formed of the united parts of the two extra limbs and bears the articulation common to the two extra tarsi. The two tarsi stand with their ventral surfaces almost at right angles to each other, but the united dorsal surfaces are almost in a continuous plane. The fifth joints alone are separate, that of RT being small (Fig. 168).

FIG. 168. Calathus grtecm, No. 776. Left anterior tibia bearing a double extra tarsus. LT, normal tarsus. RT, L'T, extra pair of tarsi. LAS, LI'S, normal anterior and posterior spurs. L'A'S', I/P'.S", anterior and posterior spurs belonging to L'T. EAS, EPS, anterior and posterior spurs belonging to HT. x, .r, dotted line indicating plane of morphological division between extra tarsi, .r.r, .r.r, plane of division between the normal and RT. (Specimen the property of Dr Ersatz.)

In studying this case one source of confusion should be specially referred to. It is seen that though the origin of the extra tarsi is posterior to the normal tarsus, the extra tarsi are as a fact united along their morphologically posterior borders. Nevertheless the position «>f tinspurs shews that it is the anterior surfaces which are morphologically adjacent to each other, for the spurs are arranged in the series A'P', P2A2, A3P3, and the union of the posterior borders of the tarsi is a result of the modification in the form of the tibia consequent on the rotation of the posterior spur.

To produce the arrangement here seen, the planes of reflexion would be M1 and M2 respectively, and these are almost at right angles to each other. Tinpre-ent case then-fore is very different from those hither- to described, t'"i- in tin-in the planes of reflexion were nearly or quite |. n.-ill.-l. \\'ln-th.-i- tlii.-, ilitli-i-i-iice in the Symmetry of the extra parts in.-iv In- i-oiinecied with tin- (li-jiarture of the normal tibia from its own customary symmetry cannot be affirmed, but such a possibility should In- bin-Hi1 in mind.

FIG. 16!). I. Ground-plan of tilrial apex of Calathus grams, No. 776. II. Similar ground-plan of the tibial apex of dilutlm* cixti'loides, No. 777. In each case the spurs are conceived as projected upon one plane, t1, the normal tarsus. .I1, I'1, its anterior and posterior spurs, t-, A-. P-, similar parts of ni-aivr i-xtra tarsus. /:), .!:;. !'••, similar parts of remoter extra tarsus. 3/1, plane of reflexion between t1 and t-. .!/'-', plane of reflexion between t- and f:t.

*777. Calathus cisteloides J; (Carabid;e): right anterior tibia bearing a pair of supernumerary tarsi compounded together. In this case the extra parts were anterior to the normal tarsus. The parts were arranged as in the diagram, Fig. 169, II, which is a projection of the liliial api'\. The apex is produced anteriorly so as to form a wide i-xpansion whirh bi-ai-s the common articulation for the double tarsus. This produced pm-timi is uf i-uiirse funned by the composition of parts i it' a pair of tibia-. It is noticeable that the three tibial apices which i-nti-r into the formation of the general apex are in one respect not actually images of each other. For the angular distances between A1 and 1", and betwrni A' and 1'-', are exceedingly small, being far less than

in a normal tibia of the species, and in fact the "moves runnin<* from i'ii each .-interior spur to the corresponding posterior one are almost parallei to each other and to the long axis of the tibia. The tarsi C- and I* separate in the first joint. The relative positions are shewn in the diagram, and it is thus seen that the planes of reflexion M1 and M'2 are inclined to each other at an acute angle. This specimen was kindly lent to me by Dr L. VON HEYDEX and was first described and figured by MOCQUERYS, CoL anorm., 1880, p. 65, Jig.

It is difficult to observe the two foregoing cases without suspecting that the fact that they deviate from the normal symmetry of extra parts may be connected with the normal modification of the anterior tibia in these Cardbidce. It should be remembered that the tibia and tarsus of the unmodified leg of a beetle are very nearly bilaterally symmetrical about the longitudinal median plane of the limb, but in this leg of these forms the symmetry is lost. Possibly then the upsetting of the ordinary rules for the Symmetry of extra parts may follow on this modification. The difference between the two cases moreover is possibly due to the fact that in one the extra parts are on the posterior surface of the leg, while in the other they are on the anterior. Since the normal limb is not bilaterally symmetrical it is reasonable to expect that the results would differ in the two cases. One other case of a pair of extra tarsi in the fore leg of a male Calathus is recorded (No. 777 a), but insufficiently described. It is to be hoped that a few cases of extra tarsi in the fore leg of male Calathus or Pterostichus may be found, and it is very possible that such a case even in Carabus would help to clear up these points.

777 a. Calathus fulvipes j (Carabida?) : tibia of right fore leg bears pair of extra tarsi. [Fig. and description inadequate.] PEKTY, Mitth. nut. Ges. Bern, iMll'i, p. 307, ./i#. 5. (10) Nine other cases departing from the Schematic Positions. *778. Platycerus caraboides (Lucan.) : left hind tarsus has form shewn in Fig. 170. The terminal joint had only one claw. AJ and L' are presumably the extra pair, but it will be seen that they arise at separate places from the 3rd tarsal joint. Otherwise, they stand approximately in Position V. Described originally by MoCQUEEYS, Col. anorin., p. 67, fig.

779. Philonthus ventralis (Staphylinidse): third joint of right posterior tarsus bearing supernumerary termination of double structure. The apex of the third joint j^ is enlarged, and at a point anterior and slightly dorsal FlG 170 to the articulation of the normal fourth joint the superpjat,/ceni!i ,.„. rulioidi-a, No. 778. Left hind tarsus from posterior surface. L, the presumably normal apex,.has only one median claw. /,' and //, arise separately from the 3rd joint. (In llouen Mus.i

numerary partarise. The fourth and fifth joints of the supernumerary tarsi an- <>f double structure, hut are not separated from each other. 'I'll-- double fifth joint hears t\vo pairs of flaws, of which the two adja- .•ciit memberan- (-(iiiijioundcd together at their bases. The plane in which on.- ji.-iir of flaws stands is about at right angles to the plane in which the other pair is placed, the opposed surfaces being ventral Mirfaces. Stated in terms of the Scheme on p. 481, the supernumerary tai^i anplaced as in the position DDA, whereas their position of origin i^ I'AA. It is noticeable that the normal fifth joint does not stand ijiiite in its usual position, hut is a little twisted so that it partial! v turns its ventral surface in an anterior direction. This specimen was described and figured by FAUVEL, h'ev. d'Ent., 1883, n. p. 93, PL ii. No. 1'. It was kindly lent to me by M. Bleuse, to whom it belongs. 7S(l. Alaus sordidus ( Klateriche): Ceylon, femur of right middle leg bears two supernumerary legs arising from its postero-dorsal surface. All three legs are somewhat abnormal in form and the principal femur is partly shrivelled at its base. At a point on the postero-dorsal surface about halfway from the apex there is a large., irregular boss from which the two extra femora diverge. Of these that which is nearest to the normal leg may he distinguished as a left leg by the planes of movement of its tibia and tarsus, while the remoter leg is a right leg. The tarsus of the latter is broken but was probably complete. The sin-faces which the extra legs present to each other are structurally anterior surfaces, but the relative positions of the three legs do not coi-respond wit h any of the positions shewn in the Scheme.

It should however lie noticed that this fact may be connected with the presence of the amorphous thickening at the point of origin of the extra femora. Specimen in Hope Collection first described and figured by WESTWOOD, Drtnitiil Kiitmiiolngy, PI. xxv. tig. 9, and mentioned Proc. Linn. Soc. 1847, p. 346. 781. Clythra quadripunctata (Phyt.): left anterior trochanter bears two supernumerary legs. Both the normal leg and the two extra ones are complete. The position of the latter is very peculiar; for, arising from the anterior surface of the trofhanter, they turn their structurally dorsal surfaces towards the anterior surface of the normal leg, which thus stands between them, one of them being above it and the other ventral to it. Of these that which is placed dorsally is structurally a /•/'//// leg, while the lower one is a Ay'/, like the normal one. Both the extra legs are also partly rotated so that their ventral surfaces are partially directed /'////v/v/.x. From these tacts it appears that the

posit i f these extra legs relatively to the normal one does not correspond with any of the positions indicated in the Scheme, and it did not seem to be possible to refer this deviation from the usual arrangement to any special malformation of any of the parts. Specimen originally described by M orufKuvs, (',,/. ,/„„/•///., p. 42, fit/. TvJ. Clytus liciatus (Long.) : right tibia reduced and thickened, being shapeless and bent . Its apex presents t wo articulations, the one anterior and the other posterior, the latter bearing a normal, 4-jointed tarsus. The anterior articulation hears a slender double tarsus, the two parts of which are fompounded in the 1st, L'nd, and 3rd joints but separate in the 4th or terminal joints. The supernumerary tarsi are very

slender and the whole thickness of their common proximal joint is even less than that of the proximal joint of the normal tarsus. The FIG. 171. Cli/tiis liciatus, No. 782. I. View of right tibia. II. Detail of the extra parts, from plantar surface, ac, ac, claws supposed to be morphologically anterior, pc, rudiments supposed to represent posterior claws. III. Enlarged view of the end of the normal tarsus. (The property of Dr Kraatz.) terminal joints of the extra tarsi are well formed, but they each bear only one fully developed claw, the claw of the adjacent side of each being only represented by a rudimentary knob. It appears at first sight that these extra tarsi are at their origin from the tibia only a single appendage and that their double nature only begins from tinthird joint. This however is not the case, for there are five spurs on the tibia, together with a small brown knob which perhaps represents the sixth spur. The tibia is greatly misshapen and the arrangement of the spurs is so amorphous that I did not succeed in determining their morphological relations. This specimen was kindly lent by Dr KRAATZ, having being first described by him in fieri, ent. Zt., 1873, xvn. p. 433, figs. 1 7 and 1 7 «.

783. Cryptohypnus riparius (Elater. ). The tibia of the right anterior leg is enlarged at its apex and bears one very large tarsal joint : this joint has two apical articulations, of which the posterior bears the remaining 4 joints of what is presumably the normal tarsus. The other articulation bears a large tarsal joint, common to a pair of complete extra tarsi. This pair of tarsi stand with their lateral p;irt.~ closely adjacent and their plantar surfaces downwards, but the other taisus which is posterior to them, and is presumably the normal, stands with its plantar surface turned backwards. This disposition differs considerably from that indicated in the Scheme. For the place of origin of the extra tarsi and their position relatively to each other is A; but the normal tarsus is twisted so that it turns its dor.-al surface forwards, towards the posterior surface of the nearer extra tarsus. For this specimen I am obliged to Dr Mason.

784 Taurhina nireus (Lamell.) : right middle tibia bearing two extra tarsi. [In the normal leg of this beetle the tibia is like that of many other Lamellicorus, presenting at its apex two sharp processes, the one anterior and the other dorsal: and ventrally two articulated spines, one anterior and the other p<>>terii»r to the tarsus. The abnormal tibia of this specimen is considerably widened at its apex, and bears in addition to the normal two processes two other processes of a similar kind separated from each other by a pair of articulated spines. Instead of a single

pair of articulated -pim-, tliis tibia bears ./IP* such spines, of which a pairstand bi-twei-n tintwo i-xtni prot-e.--- . 1 n. di-position of these spines could not be made i-li ar wit In iiit -I-M ml li L'u 1 1 -. '1 ben ore two complete tarsi ami both have their ventral sin fad-* tiirin-il downwards. Tinanterior tarsus is somewhat the smaller. I did nut succeed ill definitely detennininn the homologies of the parts in this specimen. It -Mould be spp-cially oiis,.] \ ed that while the tarsi are only two in number, suggesting that tinsii]>i •inunicrary p;ut is >•///<//.-. the spines indicate that there are here at li-a-t some .-li-mi-iiN of fuith.-r r.-pi-tition.| Specimen figured by KUAATX, l>,-ut. cut. /.(., IHH;I. xxxnt. p. 'I'll, fig. 1H, and Kindly lent by him.

7s.", Ranzania bcrtolonii 1 1. aim -llieoi ID : in the right posterior foot the last joint of tintai-ii- i- curved outwardaiipl bears six claws instead of two, and three onychia in-trad of i pin . Tinarrangement of the parts is somewhat complex and could not well In- made dear without elaborate figures. Speaking generally, the last (fifth) tar-al joint presents at its apex a large articular surface of irregular shape. This surfacibears fipur laiye claws disposed in the same direction as the normal pair of claws. Of the four claw> the two adjacent ones are in solid continuity for a part of tlii-ii length, lieinr; joined together by t-hitin much as the extra dactylopodites are in Fig. IH-I, in. It is clearly shewn that the conjoined claws are respectively the fellows of the twcp free claws, for the two extra onychia stand one upon either side of and i,|,i,i,.-ite to the cm \ature of the conjoined claws. Terminally the fifth tarsal joint bears al-o a small pair of somewhat deformed claws with which an enlarged and misshapen onychium corresponds. This specimen was kindly lent to me by M. Hi mi (P \i.i vr M: KKIIVILLE and was mentioned by him in Hull. Soc. Ent. France, Ser. I'P. vi. Is.st;, p.

*78G. Rhizotrogus aestivalis $ (Lamellicorn), bearing supernuinciary | tails <.t' double structure upon the right posterior oth tarsal (V\g. \~'l). The structure found in this case is very remarkalilf and is, I believe, in some respects unique. The tarsus is normal as tar as the extremity of the terminal joint, and the abnormality consists entirely in repetition of claws and pulvillus. The normal formation is shewn from the ventral surface in Fix'. 172, A. There is an anterior claw, a posterior claw and a small pulvillus, placed ventrally to the claws, bearing two hairs. Fix- 172. 1-5, shews the abnormal foot from the ventral side. Each claw gixe.s off from its base a ventrally-directecl supernumerary claw, and each supernumerary claw is bifid at its point. Ex- amined from below each of these extra claws is seen to bear tin, </,-<>nref> separated by a ridge, and is therefore morphologically a double structure. The next structure of importance is the puKillus. The normal pulvillus (ptd) is in place and of the usual form, but (Inrsiilly to it there is a supernumerary pulvillus (pul-) of cylindrical form and rather longer than the normal pulvillus. At its apex this extra pulvillus bears a median bifid hair with another hair on each side of it; these hairs thus prove that the extra pulvillus is morphologically double.

In this foot, therefore, a supernumerary pair of claws and a supernumerary double pulvillus are intercalated between the normal da\\s and the normal pulvillus. Hence though the repetition affects both claws and pulvilli, and the structures found are sufficient for an incomplete pair of extra feet, yet the extra part-- are disposed in the system of symmetry of the normal foot, forming, all taken together, one foot only. Specimen very kindly lent by Dr G. KllAATZ.

FIG. 172. Ehizotrogus cestivalis, No. 786. A, normal hind foot from ventral surface. B, right hind foot of No. 78C> from ventral surface. C, enlnwl view of pulvilli. D, inside view of the claws at the anterior border of the apex. E, inside view of the claws of the posterior border of the apex. A, anterior. /', posterior. a, normal anterior claw of abnormal foot, p, normal posterior of the same, a', a", the two points of extra claw of anterior side, p', p", the two corresponding posterior points. In D the posterior group of claws is supposed to be cut off at P. pul, normal pulvillus. 2nd'2, extra double pulvillus.

(11) Cases in which the leys were either mutilated, or in amorphous, or insufficiently described. 787. Want of space prevents me from giving more than a list of references to these cases. Most of them besides are imperfectly known. Of those seen by myself the case of Jlixtr,- would, I think, be interest ing, but I regret that my notes of this case are imperfect. Tn tinfollowing list the letters R and L shew the leg affected ; the t means that the case probably did not agree with the Scheme, the that it probably did agree ; the + means that the parts were either mutilated, or imperfect, or deformed. Of those unmarked, the accounts artinadequate.

1 As Kraatz suggests, this is presumably tincase given by SARTORIUS, L c. - Probably same specimen as that of CJRKDLER, Korresp. zool.-min. Ver. Regen*l>., 3 Tiedemann's grave comment is of interest as recalling past phases of thought. He says: " II "«x ilii- i'.ntxti'lnui'i tier alien lieaehriebeiii'H Misxbihliinfi bi'trijf't, *<> l''ii<xt gieh iri'hl iiiiiii'/iiin n. i/(/x.< (//,• I'liiintn.tie ih r Mutter den Mtiikiiferx durelt eiii ruriinn- ,1,'iinniieiiea 1','raeht'ii (in fiierei/t, hier niflit <;/.< I'rtuche bexehulilii/t werden kunn, t hells ireil irir Hlierltuii/it I;, iin Beweiseftlr eine Irblnifte I'huiitii.fii' tier Mnil.-iil't'r littben, nnd tin //.-,• ireil dii- r.ililiniii ilex l-'.mbriju <in**erlmlb ilex l.eiliex tier Mutter nur .-n-lir Itniiixnnt iiexeliieht. nnd die Mutter nlnieliin iileie/i nneh Lciittini der I'.ier stirbt " I. C., p. 126.

In dealing with extra antennae there is more difficulty in termining the true nature of the parts than there is in the case of extra legs. We have seen that the real duplicity of compounded extra parts often appears only in the fact that they have a l>ilateral symmetry, while in the normal appendage one side is differentiated from the other. Now in very many species of Insects the antenna seems to be a bilaterally symmetrical filament, having joints cylindrical or elliptical in section. When from such an antenna there proceeds an extra filament, itself bilaterally symmetrical, it is almost impossible to determine whether the extra filament is really a single repetition of the normal or whether it is made up of two homologous borders of a pair. (Cp. Nos. 801 and 704.) In speaking of actual cases of duplicity in Arthropodan appendages we shall have to return to this subject.

Meanwhile evidence will be given as to examples of obvious duplicity in extra antenna?. It will be seen that in species having normally a marked differentiation between the anterior1 and posterior borders of the antennae (Lamellicorns, Lucanidae, &c.), and the case has been really studied, there is often clear proof not only of the duplicity of the extra parts but also that thev are arranged as images, almost as described for legs. We shall moreover meet cases where of the paired extra parts one springs free from the normal at a point proximal to the point of origin of its fellow. Among extra legs there is scarcely any certain example of this phenomenon, Platycerus caraboides N". 778 being perhaps the clearest case. But among antenme thenare several where no other interpretation seems possible. The>e cases I have set in a separate section.

Of the remainder, little can be said with confidence. Probably if they were carefully examined microscopically it would be found that differentiation between the two sides exists in respect of the distribution of sense-organs or hairs, and that thus the duplicity and symmetry might be traced. After giving the clear cases I have thought it enough to give a list of those of this doubtful order. As has been said, there is little doubt that with careful study of the specimens many of the cases now included in the list of supposed single extra appendages might be shewn to be cases of extra parts in Secondary Symmetry.

1 This term is used, as in the case of legs, to denote the bonlt-r which is am when the appendage is extended horizontally at right anglr* to the Unly. Tlie upper surface will then be dorsal, the lower ventral. These terms are thus applied without any intention of affirming that they are morphologically correct. Phyllopertha horticola (Larnellicorn) : specimen in which the right antenna bear- a supernumerary pair of clul>s. This specimen in;iv conveniently be described in detail as it furnishes a good example of the mode in which repetition of the antennaoccurs in the Lunellicorns. The left antenna is normal and p. -------- - niiH- joints (Fig. 173, L). The first is a large pear-

-haped joint, articulating with the head by its narrow end. The id joint is also a pear-shaped joint, of about half the size of tinfirst. The third, fourth and fifth joints are elongated and <-\ lindrical. The sixth is short and wide. The seventh, eighth and ninth arc each expanded into a lamella, These three lamellaare generally kept tinnly closed together and form the sensory organ, or "club." In Melolontha (v. infra) and several other genera of Lamellicorns, there are ten joint's, of which se\en are developed as lamella-, forming the club.

In the /•/(//// antenna (Fig. 173, R), which bears the extra pair of chilis, tinbasal joint is rather thick. The second joint is longer than it normally is, and curves slightly backwards and do\\n\\ards. At its apex it bears the rest of the normal antenna, which is in all respects well formed. In addition to the normal antenna, the second joint upon its anterior surface gives attachment to a large jointwhich is imperfectly constricted into two parts in a \ertical plane at right angles to the general direction of the normal antenna. Fach of these half-joints bears a structure containing m itself all the pints proper to an antenna peripherally to the third joint, the rinks l,,.ing well-formed and normal. In absolute si/e they are eipial, but are a little smaller i han t he normal antenna.